Non-standad property attributes made flexible

Backward-incompatible changes:

• The dict_values table has been removed. The attributes column of type jsonb has been added instead to the properties table.
• The acdhOeaw\tokeneditorModel\Property::getValues() method has been removed.
• The acdhOeaw\tokeneditorModel\Property::getAttribute(attributeName) and the acdhOeaw\tokeneditorModel\Property::getAttributes() have been added.
• All non-standard property attributes from the XML schema definition are now parsed into custom attributes dictionary (stored as a jsonb in the database and available trough the API using above-mentioned acdhOeaw\tokeneditorModel\Property::getAttribute(attributeName)andacdhOeaw\tokeneditorModel\Property::getAttributes()` methods)

The change allows flexible adding of new property attributes without need to change the database structure nor the API.